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Ultrasound spectroscopy up to 6 MHz is carried out on a 12 Ah Lithium‐ion battery pouch‐cell. The analysis revealed that the attenuation behavior can be effectively described as having an absorption component and a resonance component. It was demonstrated that the absorption can be modeled as a second order polynomial. Two distinct resonances were identified at 2.2 MHz and 4.4 MHz. The first of these resonances shows a significant almost linear reduction in magnitude with increasing state of charge. By smartly choosing the ultrasound interrogation frequency to coincide with this resonance, an almost linear increase by a factor of more than five was measured in the signal amplitude between between state of charge levels of 0 and 100. This could provide the basis for a robust and straightforward state of charge determination method. [ABSTRACT FROM AUTHOR]

New ionic mesogens have been prepared based on a cyanoborate head group, which is tethered to a lipophilic periphery via a short flexible spacer. As counter ions, either tetra-n-butyl ammonium cations or sodium and potassium cations stabilized by 18-crown-6 have been used. Although all compounds exhibit SmA enantiotropic mesomorphism, X-ray diffraction, modelling and solid-state NMR uncover distinct self-assembly of the LC materials in double layers. While the ammonium ions are located between the borate anions and are in contact with spacers and aromatic units, the crown ethers with the coordinated alkali metal cations are completely nanosegregated between two borate anion layers. Homogenous and homeotropic alignment has been achieved. Electrical impedance spectroscopy reveals ionic conductivity values in the single-ion conductor that are two to three orders of magnitude higher in the correctly-aligned samples. Values of ca. 104 S cm1 in the SmA phase at 85 1C and 105 S cm1 at 40 1C have been obtained. [ABSTRACT FROM AUTHOR]

Aqueous processing of state‐of‐the‐art cathode materials for lithium‐ion batteries like LiNi0.8Mn0.1Co0.1O2 (NMC811) has evolved as a more sustainable and cost‐effective alternative to the conventional 1‐methyl‐2‐pyrrolidone‐based process. However, the implementation of aqueous processing is challenging due to the water sensitivity of nickel‐rich layered oxides. This study investigates the influence of a phosphate‐based NMC811 surface coating on the performance of aqueous‐processed NMC811 cathodes in 3 Ah cells. The results show that the cells with phosphate‐coated NMC811 outperform those with uncoated NMC811, i. e., they exhibited higher initial capacity and improved capacity retention during cycling. Post‐mortem characterization techniques reveal that the phosphate coating limits the lithium loss during aqueous cathode manufacturing and further reduces side reactions during cycling, resulting in a smaller increase of cell impedance. [ABSTRACT FROM AUTHOR]

Metallopolymers (MEPEs) show a strong absorption band attributed to a metal‐to‐ligand charge transfer (MLCT) transition. Fe‐MEPE and Ru‐MEPE thin films switch reversibly from blue‐purple (λmax=584 nm, Fe2+) to colorless (Fe3+) or orange (λmax=518 nm, Ru2+) to pale green (Ru3+). The addition of multi‐walled carbon nanotubes (MWCNTs) enhances the electrochromic (EC) properties of Fe‐ and Ru‐MEPE electrodes in several ways: (1) faster response for bleaching/coloring; (2) enhanced Coulombic efficiency; and (3) improved cycling stability, particularly for Ru‐MEPE. Moreover, the charge density of the thin film electrodes can be increased upon the addition of the MWCNTs. This performance improvement is demonstrated in electrochromic devices (ECDs) with titanium‐doped vanadium oxide (TiVOx) as the optically‐passive ion storage layer. The visible light transmittance τv values of the ECDs are improved by the addition of the MWCNTs from 20 %/56 % to 17 %/56 % and from 31 %/47 % and 34 %/55 % in the dark/bright state, for Fe‐MEPE and Ru‐MEPE, respectively. Thus, the addition of MWCNTs to Fe‐ or Ru‐MEPE is a very promising route for future fast‐switching EC applications, e. g., displays, sunroofs, and rear‐view mirrors. [ABSTRACT FROM AUTHOR]

State‐of‐the‐art methods to monitor the degree of wetting of lithium‐ion batteries during production, which are applicable at an industrial scale, are not capable of determining the spatial electrolyte distribution in the porous network of electrodes and separator. Ultrasound can bridge this gap as it has previously been proven to be a suitable method to monitor or evaluate the infiltration of porous structures, for example, epoxy resin in carbon fiber composite. Herein, the acoustic properties of different battery cell materials are evaluated over a wide frequency range in both the dry and wet states, for the first time. Furthermore, a collection of input parameters, from the experimental setup and the evaluation routine to the acoustic parameters of the battery materials themselves, are provided. These parameters are needed for the adaptation of ultrasonic nondestructive testing to the monitoring of the wetting process of a lithium‐ion battery. Most importantly, this work demonstrates that a large change in the sound velocity (up to 100%) is observed when the porous structure of a lithium‐ion battery is filled with electrolyte and thus can serve as an appropriate evaluation figure of merit. [ABSTRACT FROM AUTHOR]

Lithium metal is considered as the 'holy‐grail' among anode materials for lithium‐ion batteries, but it also has some serious drawbacks such as the formation of dendritic and dead lithium. In this study, the interplay of external pressure and different carbonate‐ and ether‐based electrolytes on the (ir)reversible expansion of lithium metal during cycling against lithium titanate and lithium iron phosphate is studied. In carbonate‐based electrolytes without any additives, lithium metal shows tremendous irreversible expansion and significant capacity reduction at elevated current densities due to the formation of mossy and dead lithium. The addition of fluoroethylene carbonate can reduce irreversible expansion and capacity reduction, especially when a high external pressure is applied. When an ether‐based electrolyte is used, the irreversible dilation of the lithium metal is suppressed when applying increased external pressures. Overall, increased external pressure appears to reduce the formation of mossy and dead lithium and improve the performance. [ABSTRACT FROM AUTHOR]

Semiconductor quantum dots are at the forefront of materials science chemistry with applications in biological imaging and photovoltaic technologies. We have developed a simple laboratory experiment to measure the quantum-dot size from fluorescence spectra. A major roadblock of quantum-dot based exercises is the particle synthesis and handling; the former requires dangerous chemicals while the later can lead to sample degradation. We overcome these drawbacks by using commercially available quantum dots. The samples are composed of CdSe-ZnS core-shell nanoparticles embedded in a polymer matrix. A fluorescence spectrophotometer is used to collect photoluminescence data and the subsequent calculations are straightforward. Student feedback indicates that these experiments provide a new understanding of quantum mechanics and the particle-in-a-box model. We are able to examine the role of spectroscopy in chemical investigations and a cause of spectroscopic line broadening. (Contains 1 table and 2 figures.)